copy con:

Before DOS 5.01 and the inception of edit.com (may have been edit.exe, however I'm not willing to pull out an old DOS disk set and find out), it was nearly impossible to write or edit text files with the default DOS installation. There were utilites printed in magazines, and distributed on diskettes that allowed for the manipulation of simple text files, but the only one that was included with DOS was edlin, and those who have successfuly used this program hardly live to tell of it. So, copycon was the way to go if you needed to edit config.sys to get an extra 10k of upper memory free.